Sam Altman, president of seed accelerator Y-Combinator, recently asked a very basic question of his Twitter followers: What could someone have taught you in a class about startups that would have made you a better founder? Within half an hour, he'd received over 50 responses from entrepreneurs across the network. Some were concrete (e.g., "Taxes. How do they even work?"), while others were more abstract (e.g., "communication and empathy.") Here are 10 of the most noteworthy answers, from business owners who learned the hard way: